A local area network system or loop distribution plant is effective to connect each telephone customer to a central office through a transmission medium. Presently, the transmission medium commonly is a twisted pair of insulated copper conductors which, for most of its length, is disposed in a multipair cable.
In a typical loop plant, a main feeder cable connects the central office to an area to be served. Branch feeder cables extend from the main cable to designated areas. Each branch cable connects to a plurality of distribution cables that extend service to a particular customer area. A distribution service or drop cable connects a distribution cable to each customer premises.
The loop plant has evolved as new materials, methods and plant concepts were developed to provide reliable telephone service at a reasonable cost. Loop plant must be inexpensive to install and maintain, should require a relatively small amount of physical space, and be readily accessible to accommodate changes in service and in customers.
Today, efforts are under way to cause the loop to become one in which optical fiber plays a predominant role. As is known, optical fiber interface electronic devices which are required for an optical fiber loop are not yet generally available. When such devices become available, loop architecture and media also should be available so that devices can be connected immediately into the loop. Accordingly, it becomes important to provide a system which will provide service from those optical devices now in development to customer premises.
Such a system has been developed. The cornerstone of the system insofar as a particular area is concerned is a distribution center which is referred to as a remote terminal. For the loop distribution plant, each remote terminal is designed to provide service to a plurality of distribution points. Optical fiber is to be extended from optical units of the remote terminal to an interconnection portion whereat it is connected to runs which extend to branch-outs. At each branch-out, an incoming optical fiber is connected, for example, by a prealigned rotary splice shown in U.S. Pat. No. 4,691,986 which issued on Sept. 9, 1987 in the names of J. A. Aberson, et al. to a distribution drop. From a distribution drop, service is provided by a drop cable to each of a plurality of homes in a subdivision, for example.
Inside the remote terminal are a number of frames, with each frame adapted to receive a plurality of cards. Each card which includes a laser, a splitter and a detector, for example, is adapted to be connected through a coupling which is mounted in a panel to a jumper cable which extends to the interconnection portion of the remote terminal. Such a panel is referred to commonly as a backplane. For this purpose, the card may be provided with a modified ST.RTM. connector, for example. For the loop distribution plant as now envisioned, not only is such a backplane provided at the remote terminal, but also one would be found at each home.
A jumper which is terminated at each of its ends with an ST.RTM. connector, for example, extends from an opposite or outgoing side of the backplane coupling to an optical connection portion of the remote terminal. The optical connection portion allows interconnections and/or cross connections of a connector end of each jumper cable to an optical fiber of a cable which extends outwradly to the branch-outs of the loop plant. The connections from the jumper cables to the optical fibers of the outgoing cable may be made, for example, by means of a fanout arrangement shown in U.S. Pat. No. 4,305,642 which issued on Dec. 15, 1981 in the names of L. B. Bloodworth, et al.
The outgoing cable from the interconnection portion of the remote terminal extends to a primary closure. From the primary closure, smaller cables extend to intermediate closures and thence to drop closures such as those disclosed and claimed in application Ser. No. 155,194 which was filed on Feb. 12, 1988 in the names of R. R. Ross and I. Vedejs now U.S. Pat. No. 4,820,007. Each of the drop closures is adapted to provide service to a plurality of customer premises.
It is anticipated that each home will be provided with a service unit mounted on the exterior of the home. Each of these units will include a panel-mounted backplane coupling adapted to receive an ST.RTM. connector, for example, at one end thereof. An opposite end of the backplane coupling, which may be the same as that coupling which is mounted in the remote terminal, is adapted to receive a modified ST.RTM. connector which terminates a lead from a card-mounted splitter.
One of the problems in a loop arrangement such as that just described relates to the mounting of the cards within the remote terminal. For example, the center-to-center spacing may be as low as 0.441 inch. Each card must be capable of being inserted repeatedly to provide a low-loss, low reflection optical connection, and yet there is very little room in which a craftsman can make a connection. Obviously, the sought-after coupling also must be rugged and must insure that alignment of the ST.RTM. connectors occurs albeit accomplished in the confines of a congested backplane.
Typically, each card is connected to the backplane coupling by a craftsman who causes the card to be moved into a slotted opening in a frame. The card is caused to be moved toward the coupling until the modified ST.RTM. connector at its leading end is inserted into one end of its associated coupling and then into one end of an alignment sleeve which is disposed within the coupling.
Considering the space involved, it should be readily apparent that the connector insertion is a blind one, that is the craftsman cannot view directly the coupling as the card connector is moved toward it. Blind insertion raises two problems. First, a physical insertion must take place, otherwise the end face of the connector could be damaged, and/or no optical connection will take place. Also, a frequent happening is an excessively angled insertion of the connector plug into the coupling which may cause the sleeve to break. Further, the canting of the connector with respect to the sleeve results in misalignment with the connector plug at an opposite end of the coupling as well as excessive reflection.
Connective arrangements in the prior art have not been altogether successful in meeting the needs identified hereinbefore. Some have included sleeves mounted in the backplane, but the frequency of broken sleeves upon insertion of the cards has been high. In others, alignment of the optical fibers has suffered, resulting in unacceptably high losses.
Seemingly, the prior art has not recognized nor addressed this problem. And yet it must be solved for reliable, low loss optical transmission to be brought to the home. What is sought is a coupling arrangement which facilitates the connection of a card, on which are mounted optical devices, to an optical fiber. Obviously, the coupling arrangement must be relatively inexpensive and easily installed. Further, it must facilitate the interconnection with low probability of sleeve breakage of connector fiber damage and must result in low reflection and low insertion loss.